Which muscle group is primarily responsible for extending the knee joint?

• A. Quadriceps femoris group
• B. Hip adductor group
• C. Hamstring group
• D. Gastrocnemius and soleus (triceps surae)

Answer: (A)

Verified step by step guidance

1. Step 1: Understand the movement involved. Extending the knee joint means straightening the leg at the knee, increasing the angle between the thigh and the lower leg.
2. Step 2: Identify the primary muscles responsible for knee extension. The quadriceps femoris group, located at the front of the thigh, is the main muscle group that extends the knee.
3. Step 3: Recognize the roles of other muscle groups listed. The hamstring group primarily flexes the knee (bends it), the hip adductor group mainly brings the thigh toward the body's midline, and the gastrocnemius and soleus muscles primarily act on the ankle joint (plantarflexion).
4. Step 4: Confirm that the quadriceps femoris group includes four muscles (rectus femoris, vastus lateralis, vastus medialis, and vastus intermedius) that work together to extend the knee joint.
5. Step 5: Conclude that since the quadriceps femoris group is the only group primarily responsible for knee extension, it is the correct answer.